On 26 May, the garrison of the Rupel Fortress detected approaching German – Bulgarian columns. Its commander, Major Ioannis Mavroudis , after notifying his superiors (6th Division and Thessaloniki Fortress Command), informed the approaching Germans of his orders to resist. The 6th Division commander, Major General Andreas Bairas , mobilized his forces and issued orders to resist any attack, while sending word to Athens, IV Corps, and notifying the Allied forces that had advanced up to the village of Strymoniko (about 40 kilometers (25 mi) to the south) for possible assistance. Despite repeated warnings that they would resist any attempt to seize Rupel, and that Athens had been notified, three German – Bulgarian columns moved to capture Mount Kerkini, Mount Angistro, and the bridge over the Strymon at Koula, until Mavroudis ordered his guns to open fire upon them. They then halted and withdrew back over the border.
